<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>CSS3选择器</title>
<style>
	li:nth-child(3n){ background : red; }
</style>
</head>
<body>
<ul>
	<li>HTML</li>
    <li>CSS</li>
    <li>JavaScript</li>
    <li>HTML</li>
    <li>CSS</li>
    <li>JavaScript</li>
</ul>
</body>
</html>
